/*========================== begin_copyright_notice ============================

Copyright (C) 2024 Intel Corporation

SPDX-License-Identifier: MIT

============================= end_copyright_notice ===========================*/

// This pass attempts to reduce number of times FP rounding mode is switched by
// moving and grouping together instructions using the same rounding mode.
// This pass works after optimizations, before emitter. Instructions are
// reordered only in the same basic block, with optional distance limit for move.

#include "Compiler/CISACodeGen/FPRoundingModeCoalescing.hpp"

#include "Compiler/CodeGenPublic.h"
#include "Compiler/IGCPassSupport.h"
#include "Compiler/MetaDataUtilsWrapper.h"
#include "common/igc_regkeys.hpp"

using namespace llvm;
using namespace IGC;
using namespace IGC::IGCMD;

#define DEBUG_TYPE "fp-rounding-mode-coalescing"

// Represents collection of FP instructions with the same RM. RM is not switched
// between the first and the last instruction in the group.
class FPRoundingModeGroup {
public:
  FPRoundingModeGroup(Instruction *I, ERoundingMode RM) : Head(I), Tail(I), RM(RM) { Instructions.insert(I); }

  ERoundingMode getRoundingMode() const { return RM; }

  Instruction *getHead() const { return Head; }

  bool contains(Instruction *I) const;
  bool uses(Instruction *I) const;

  void setHead(Instruction *I);
  void insertAfterGroup(Instruction *I);
  bool comesBeforeTail(Instruction *I);

private:
  // First custom RM FP instruction in the group.
  Instruction *Head = nullptr;

  // Last custom RM FP instruction. If instruction to insert to group has
  // uses that are FP instructions in different RM mode than this
  // group, these instructions would be moved here.
  //
  // Example:
  //   %fma.rtz.1.result = call double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %0, double %1, double %2) ; <-
  //   To insert %tmp = fadd double %0, %fma.rtz.1.result ; <- instruction in different RM %fma.rtz.2.result = call
  //   double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %3, double %4, double %5) ; <- HEAD %fma.rtz.3.result =
  //   call double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %6, double %7, double %8) ; <- TAIL
  //
  // Because %tmp depends on the result of instruction to move, the FP instructions would be reordered to:
  //
  //   %fma.rtz.1.result = call double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %0, double %1, double %2) ; <-
  //   new HEAD %fma.rtz.2.result = call double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %3, double %4, double
  //   %5) ; %fma.rtz.3.result = call double @llvm.genx.GenISA.fma.rtz.f64.f64.f64.f64(double %6, double %7, double %8)
  //   ; <- TAIL %tmp = fadd double %0, %fma.rtz.1.result
  //
  // Because only FP instructions are expected to be moved, there should be no impact on latency on FP pipe.
  Instruction *Tail = nullptr;

  SmallPtrSet<Instruction *, 4> Instructions;

  const ERoundingMode RM;
};

// Attempts to reorder FP instructions in one basic block.
class FPRoundingModeCoalescingImpl {
public:
  FPRoundingModeCoalescingImpl(ModuleMetaData *MMD, BasicBlock &BB) : MMD(MMD), BB(BB) {}

  bool coalesce();

private:
  bool update();

  bool setsRoundingMode(Instruction &ToMove);

  bool checkMoveThreshold(Instruction &ToMove, Instruction *InsertPoint);

  bool tryMove(Instruction &ToMove);

  bool tryMove(Instruction &ToMove, FPRoundingModeGroup &InsertPoint);

  ModuleMetaData *const MMD;
  BasicBlock &BB;

  SmallVector<FPRoundingModeGroup, 8> Groups;

  SmallPtrSet<Instruction *, 32> VisitedInstructions;
};

class FPRoundingModeCoalescing : public llvm::FunctionPass {
public:
  static char ID;

  FPRoundingModeCoalescing();

  virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
    AU.setPreservesCFG();
    AU.addRequired<MetaDataUtilsWrapper>();
    AU.addPreserved<MetaDataUtilsWrapper>();
  }

  bool runOnFunction(llvm::Function &F) override;

  virtual llvm::StringRef getPassName() const override { return "FPRoundingModeCoalescing"; }
};

// Utility function to move instruction + log.
void moveAfter(Instruction *I, Instruction *InsertPoint) {
  LLVM_DEBUG(dbgs() << "Moving ["; I->print(dbgs(), true); dbgs() << "] after ["; InsertPoint->print(dbgs(), true);
             dbgs() << "]\n");
  I->moveAfter(InsertPoint);
}

bool FPRoundingModeGroup::contains(Instruction *I) const { return Instructions.count(I); }

bool FPRoundingModeGroup::uses(Instruction *I) const {
  for (auto V = I->users().begin(); V != I->users().end(); ++V) {
    if (auto *User = dyn_cast<Instruction>(*V)) {
      if (this->contains(User))
        return true;
    }
  }
  return false;
}

// Sets instruction as new head of the group, without moving it.
void FPRoundingModeGroup::setHead(Instruction *I) {
  LLVM_DEBUG(dbgs() << "Setting ["; I->print(dbgs(), true); dbgs() << "] as new head before [";
             Head->print(dbgs(), true); dbgs() << "]\n");
  Head = I;
  Instructions.insert(I);
}

// Moves given instruction after last instruction in group. Does not expand group.
void FPRoundingModeGroup::insertAfterGroup(Instruction *I) {
  LLVM_DEBUG(dbgs() << "Moving ["; I->print(dbgs(), true); dbgs() << "] after tail ["; Tail->print(dbgs(), true);
             dbgs() << "] (head is ["; Head->print(dbgs(), true); dbgs() << "])\n";);
  I->moveAfter(Tail);
}

// Returns true if given instruction comes before group's tail.
bool FPRoundingModeGroup::comesBeforeTail(Instruction *I) { return IGCLLVM::comesBefore(I, Tail); }

// Returns true if at least one change is made in basic block.
bool FPRoundingModeCoalescingImpl::coalesce() {
  bool result = false;

  // Repeat until nothing can be moved.
  while (true) {
    if (update()) {
      result = true;
    } else {
      break;
    }
  }

  return result;
}

bool FPRoundingModeCoalescingImpl::update() {

  for (auto I = BB.rbegin(); I != BB.rend(); ++I) {

    if (VisitedInstructions.insert(&*I).second == false)
      continue;

    if (!setsRoundingMode(*I))
      continue;

    ERoundingMode RM = GetRoundingMode_FP(MMD, &*I);

    // For safety reasons limit transformation to only one non-default RM.
    if (!Groups.empty() && Groups.begin()->getRoundingMode() != RM)
      continue;

    if (tryMove(*I))
      return true;

    // Instruction can't be moved, create new group.
    Groups.emplace_back(&*I, RM);
  }

  return false;
}

// Returns true if given instruction will change rounding mode.
bool FPRoundingModeCoalescingImpl::setsRoundingMode(Instruction &ToMove) {
  if (!setsRMExplicitly(&ToMove))
    return false;

  // Instruction sets explicit rounding mode. But this mode might already match default one
  // in kernel, so there might be no need to change it.

  ERoundingMode RM = GetRoundingMode_FP(MMD, &ToMove);
  ERoundingMode ConvRM = GetRoundingMode_FPCvtInt(MMD, &ToMove);

  return (RM != static_cast<ERoundingMode>(MMD->compOpt.FloatRoundingMode) && RM != ERoundingMode::ROUND_TO_ANY) ||
         (ConvRM != static_cast<ERoundingMode>(MMD->compOpt.FloatCvtIntRoundingMode) &&
          ConvRM != ERoundingMode::ROUND_TO_ANY);
}

bool FPRoundingModeCoalescingImpl::checkMoveThreshold(Instruction &ToMove, Instruction *InsertPoint) {
  unsigned Dist = 1;
  for (Instruction *I = ToMove.getNextNonDebugInstruction(); I != InsertPoint;
       I = I->getNextNonDebugInstruction(), ++Dist) {
    if (Dist >= IGC_GET_FLAG_VALUE(FPRoundingModeCoalescingMaxDistance))
      return false;
  }

  return true;
}

// Returns true if instruction is moved.
bool FPRoundingModeCoalescingImpl::tryMove(Instruction &ToMove) {
  for (auto &InsertPoint : Groups) {
    if (tryMove(ToMove, InsertPoint))
      return true;
  }

  return false;
}

// Attempts to move given instruction on top of group of other FP instructions.
// Returns true if instruction is moved.
bool FPRoundingModeCoalescingImpl::tryMove(Instruction &ToMove, FPRoundingModeGroup &Group) {

  if (GetRoundingMode_FP(MMD, &ToMove) != Group.getRoundingMode())
    return false;

  // First collect all uses of instruction to move that are before group's tail.
  // In case instruction will have to be moved, uses will have to be moved too.
  // Keep uses sorted in order of occurence in LLVM IR.
  auto Cmp = [](Instruction *a, Instruction *b) { return IGCLLVM::comesBefore(a, b); };
  std::set<Instruction *, decltype(Cmp)> Users(Cmp);

  SmallVector<Instruction *, 8> worklist;
  SmallSet<Instruction *, 8> visited;
  worklist.push_back(&ToMove);
  while (!worklist.empty()) {
    Instruction *ToCheck = worklist.back();
    worklist.pop_back();
    auto [_, inserted] = visited.insert(ToCheck);
    if (!inserted) {
      continue;
    }
    for (auto V = ToCheck->users().begin(); V != ToCheck->users().end(); ++V) {
      if (auto *I = dyn_cast<Instruction>(*V)) {
        if (I->getParent() != ToMove.getParent())
          continue;
        if (isa<PHINode>(I))
          continue;
        // Special case - if group directly uses ToMove, then this use is already on correct position.
        if (Group.comesBeforeTail(I) && (ToCheck != &ToMove || !Group.contains(I))) {
          Users.insert(I);
          worklist.push_back(I);
        }
      }
    }
  }

  // Now that all users are collected, count how many users would switch RM.
  int UsersSwitchingRM = 0;
  for (auto *I : Users) {
    if (!ignoresRoundingMode(I) && GetRoundingMode_FP(MMD, &ToMove) != GetRoundingMode_FP(MMD, I))
      ++UsersSwitchingRM;
  }

  // Next, find first instruction before group switching RM that is NOT an user
  // of instruction to move. This will be an insert point.
  Instruction *InsertPoint = nullptr;
  for (Instruction *I = Group.getHead()->getPrevNonDebugInstruction(); I != &ToMove;
       I = I->getPrevNonDebugInstruction()) {
    if (!ignoresRoundingMode(I) && Users.count(I) == 0) {
      InsertPoint = I;
      break;
    }
  }

  // If there is no insert point and no user switching rounding mode, then it means there is
  // no change in RM between instruction to move and group. There is need to move.
  if (InsertPoint == nullptr && UsersSwitchingRM == 0) {
    Group.setHead(&ToMove);
    return true;
  }

  // A move is needed. Before any move, check move threshold.
  if (!checkMoveThreshold(ToMove, InsertPoint ? InsertPoint : Group.getHead()))
    return false;

  // Check if there are any users not suitable for move.
  if (std::find_if(Users.begin(), Users.end(),
                   [](Instruction *I) { return I->mayReadOrWriteMemory() || I->mayHaveSideEffects(); }) != Users.end())
    return false;

  // Reordering too much could have an impact on latency, so consider only two scenarios:
  // 1. If there are no uses depending on RM, then all uses will be moved after insert point, BEFORE group.
  //    Higher number of impacted instructions keep their original order.
  // 2. If at least one user depends on RM, in order to minimize number of times RM is switched, all instructions
  //    are moved AFTER group.

  if (UsersSwitchingRM > 0) {

    // Move all uses after group. First check if this is safe - instruction can't be moved
    // if it is already a part of the group or is used by group's member.
    if (std::find_if(Users.begin(), Users.end(), [&](Instruction *I) { return Group.contains(I) || Group.uses(I); }) !=
        Users.end())
      return false;

    for (auto It = Users.rbegin(); It != Users.rend(); ++It)
      Group.insertAfterGroup(*It);

  } else {
    // All uses to move ignore RM. They can be moved after insert point, before group.
    // Better preserves original order of instructions.
    for (auto It = Users.rbegin(); It != Users.rend(); ++It) {
      if (IGCLLVM::comesBefore(*It, InsertPoint))
        moveAfter(*It, InsertPoint);
    }
  }

  if (InsertPoint)
    moveAfter(&ToMove, InsertPoint);

  Group.setHead(&ToMove);

  return true;
}

FPRoundingModeCoalescing::FPRoundingModeCoalescing() : FunctionPass(ID) {
  initializeFPRoundingModeCoalescingPass(*PassRegistry::getPassRegistry());
}

bool FPRoundingModeCoalescing::runOnFunction(Function &F) {
  LLVM_DEBUG(dbgs() << "Running on function " << F.getName() << ", FPRoundingModeCoalescingMaxDistance="
                    << IGC_GET_FLAG_VALUE(FPRoundingModeCoalescingMaxDistance) << "\n");

  auto *MMD = getAnalysis<MetaDataUtilsWrapper>().getModuleMetaData();

  bool result = false;

  for (auto &BB : F) {
    result |= FPRoundingModeCoalescingImpl(MMD, BB).coalesce();
  }

  return result;
}

char FPRoundingModeCoalescing::ID = 0;

#define PASS_FLAG "igc-fp-rounding-mode-coalescing"
#define PASS_DESCRIPTION "Groups FP instructions with common rounding mode"
#define PASS_CFG_ONLY false
#define PASS_ANALYSIS false
IGC_INITIALIZE_PASS_BEGIN(FPRoundingModeCoalescing, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)
IGC_INITIALIZE_PASS_DEPENDENCY(MetaDataUtilsWrapper)
IGC_INITIALIZE_PASS_END(FPRoundingModeCoalescing, PASS_FLAG, PASS_DESCRIPTION, PASS_CFG_ONLY, PASS_ANALYSIS)

FunctionPass *IGC::createFPRoundingModeCoalescingPass() { return new FPRoundingModeCoalescing(); }
